President Barack Obama addresses the Democratic National Convention in Charlotte, N.C., on Thursday.

J. Scott Applewhite/AP

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Like Lord Voldemort in the Harry Potter saga, climate change has been the issue "that shall not be named" – mostly a political no-show in the presidential campaign.

But that may be changing thanks to the political heat generated by the two conventions.

In Tampa, Mitt Romney threw down the gauntlet to Barack Obama, for whom global warming – and the consequent sea level rise – has been a signature issue since he promised in 2008 to do something about it as president.

"President Obama promised to begin to slow the rise of the oceans and heal the planet," Mr. Romney told GOP delegates in Tampa, a smile on his face. "My promise [long pause – audience laughter] is to help you and your family."

But that laugh line appears to have been just too much for Mr. Obama, who is fighting for support in a neck-and-neck campaign where the economy – not climate change – is the front and center issue. So he let fly.

"Yes, my plan will continue to reduce the carbon pollution that is heating our planet – because climate change is not a hoax," the president shouted to delegates in Charlotte, N.C. "More droughts and floods and wildfires are not a joke. They're a threat to our children's future. And in this election, you can do something about it."

That high-profile statement, political analysts say, may have marked a major turnabout for the president, who has scarcely mentioned global warming – or the more scientific designation of "climate change" – in recent months.

Ever since an attempt to pass cap-and-trade legislation to limit greenhouse gas emissions failed in 2010, the president has seemed almost mute on the topic – with a few rare exceptions mostly when speaking overseas, frustrated environmentalists say.

"Two years ago the White House communications shop decided this was not a good issue to talk about," says Joe Romm, a senior fellow at the Center for American Progress Action Fund and a former acting assistant secretary of energy. His blog, called "Climate Progress," has tracked the issue closely.

"My guess is that Obama, who is an incredibly competitive guy, was just annoyed at mockery and laughter and wanted to respond personally," Mr. Romm says. "But I also think that he's been trying to think about how to inject climate into the debate. Romney gave him an opening to do just that."

But there are also indications that Obama, scratching for support among independent voters in Ohio, Iowa, and other swing states, may have been warming to the idea of once again more publicly embracing climate change.

"It's been easy for the other side to pour millions of dollars into a campaign to debunk climate-change science," Obama told Rolling Stone magazine in April. "I suspect that over the next six months, [climate change] is going to be a debate that will become part of the campaign, and I will be very clear in voicing my belief that we’re going to have to take further steps to deal with climate change in a serious way."

Be that as it may, Obama and his campaign would be unlikely to be so undisciplined as to get into a national high-profile fight over climate policy if he were going to lose credibility with a public more hungry for jobs than fixing global warming.

But what if climate change turned out to be a good issue – not a boat anchor? That's exactly what public opinion researchers at George Mason, Yale, and Stanford universities have been finding in national polls last year and this year.

In a nonpartisan national poll released by George Mason and Yale in March, 72 percent of Americans surveyed said global warming should be a very high (12 percent), high (28 percent), or medium (32 percent) priority for the president and Congress. Among registered voters, 84 percent of Democrats, 68 percent of independents, and 52 percent of Republicans said global warming should be a priority.

What those and other numbers mean, says the man who analyzed them, is that Obama and other Democratic candidates, instead of paying a political penalty for hitting global warming as an issue on the campaign trail – actually benefit.

"Our polling shows that in swing states, Democratic candidates who take a pro-climate-action stance will find it to be a vote winner for them," says Edward Maibach, director of the Center for Climate Change Communication at George Mason University in Virginia, who produced the poll. "The extra votes will come from independents."

Unfortunately for Romney, even if he were to win support among independents by raising global warming as a problem to deal with, it would weaken support among his conservative base, researchers say.

"Independents respond to climate change as an issue much more like Democrats than Republicans," he says. "But for a Republican candidate, taking a pro-climate action station in a general election campaign is neutral impact – winning independent votes, but losing some conservative support."

Similarly large numbers support renewable energy development as a way to reduce greenhouse gas emissions and curb global warming, a point that Obama also hammered in his speech.

Even before his acceptance speech there were signs Obama was warming to the idea of talking about climate change once again. In Iowa, where climate-friendly wind-turbine manufacturing is big business, Obama has hammered Romney for opposing tax credits that would help keep factories open. And in three college appearances in recent weeks, the president has highlighted global warming to those audiences, which polls show are quite receptive to that message, Romm says.

For his part, Romney has since the Tampa convention repeated his applause line while stumping for votes. And he and Obama squared off in an on-line matchup on climate change on the Science Debate website on Tuesday. So now it seems, climate change may well be headed back onto the menu for political debate this fall.

"I don't know what the president or his advisers' thoughts were about the issue, but one thing is certain, the president had not been talking about issue of climate change publicly in quite some time," Dr. Maibach says. "Now he seems ready to speak out again about it. Maybe he saw some of our results and realized talking about global warming was a good idea."